1. Field of the Invention
This invention relates to a bar-code symbol reading apparatus, and more particularly to a bar-code symbol reading apparatus using a two-dimensional imaging device such as a video camera.
2. Description of the Related Art
Today, bar code symbols have been used in many countries and are available in a variety of types. Some of typical bar code symbols are JAN/UPC/EAN code, ITF (interleaved 2 of 5) code, CODE 39, NW-7 code, and CODE 128. To meet the recent demands that a bar code should carry more information and be stuck in a smaller space, two-dimensional bar code symbols with a large amount of information and a higher recording density have been proposed. Among such two-dimensional bar code symbols are CODE 16K, CODE 49, PDF 417, and DATA CODE.
There are various types of reading apparatuses for one-dimensional bar code symbols such as JAN/EAN code, ITF (interleaved 2 of 5) code, CODE 39, NW-7 code, CODE 128. The reading techniques for such one-dimensional code symbols have already been established. Some of typical types of such apparatuses are a pen type, a touch type, and a laser type. On the other hand, there are presently few types of apparatuses for two-dimensional bar-code symbols and reading techniques for reading these symbols have not been established yet.
The fundamentals of two-dimensional bar-code symbol reading techniques are almost the same as those of conventional one-dimensional bar-code symbol reading techniques. Specifically, light is projected from a light source onto a bar code symbol and the reflected light from the symbol is gathered to a light-receiving element in the reading apparatus. The gathered signal is decoded by an electric circuit made up of a microcomputer to read the bar code symbol.
One type of two-dimensional bar-code symbol reading apparatuses is a stand type (a fixed type). In this type, a bar-code symbol reading apparatus is secured and the operator puts a bar-code symbol-recorded sheet or article under the reading apparatus and has the apparatus read the symbol.
The stand-type bar-code symbol reading apparatus comprises a camera stand, a decoder box, and a monitor.
The camera stand is composed of a video camera, supports for propping up the video camera, and a base plate on which the operator is to place a bar-code symbol-recorded sheet or article.
The decoder box receives the output of the video camera via a camera cable, decodes the video camera output signal into the contents of the recorded bar code symbol, and transfers the contents to a host computer, a terminal equipment, or the like.
The monitor receives the video output of the decoder box and is used for the operator to make sure that the bar code symbol recorded on the sheet or article is completely within the field of view of the video camera. The monitor is necessary when a bar code symbol is large.
With such an apparatus where the bar code symbol recorded on the sheet or article is checked on the monitor to see if it is completely within the field of view of the video camera, the operator must judge whether or not the bar code symbol is within the field of view, while watching the monitor screen. The criterion of the judgment differs widely from operator to operator; even if they look at the same screen display, an operator may proceed to perform the decoding process without the slightest hesitation but another operator may place the bar-code symbol-recorded sheet or article again correctly. In the former case, even if decoding cannot be effected, the operator starts the decoding process and, when he hears the buzzer sound to inform him that decoding cannot be effected, he places the bar-code symbol-recorded sheet or article again, with the result that the time spent in decoding is wasted. In the latter case, even if the bar code symbol is not completely within the field of view of the video camera or is partly out of the field, the decoding can sometimes be effected. In this case, the operator places the bar-code symbol-recorded sheet or article again although the decoding can be achieved, with the result that the time and labor required for replacement is wasted.